Minerals with a palmierite-type structure. Part I. Mazorite Ba₃(PO₄)₂, a new mineral from the Hatrurim Complex in Israel

The new mineral mazorite, ideally Ba₃(PO₄)₂, a P-analogue of gurimite Ba₃(VO₄)₂, was discovered in rankinite paralava hosted by the massive gehlenite-bearing pyrometamorphic rocks of the Hatrurim Complex in Israel. It has also recently been discovered in xenolith samples from the Bellerberg volcano in Germany. Holotype mazorite usually forms colourless plate-like crystals up to 70–100 μm in length but also occurs in small aggregates in association with other rare Ba-bearing minerals such as zadovite, celsian, hexacelsian, bennesherite, sanbornite, walstromite, fresnoite, gurimite, alforsite and barioferrite. The mineral is transparent, exhibits vitreous lustre and has a good cleavage on (001). Optically, mazorite is uniaxial (+), with ω = 1.760(3) and ε = 1.766(3) (λ = 589 nm). The empirical formula of the holotype mazorite calculated on 8O is (Ba_2.69K_0.22Na_0.04Ca_0.02Sr_0.01)_Σ2.98(P_1.16V_0.57S_0.24Al_0.04Si_0.03)_Σ2.04O₈. Mazorite crystallises in space group R^̿3m, with unit-cell parameters a = 5.6617(5) Å, c = 21.1696(17) Å, V = 587.68(9) ų and Z = 3. Its crystal structure consists of BaO₁₂, BaO₁₀, and PO₄ polyhedra, ordered along the c-axis in PO₄–BaO₁₀–BaO₁₂–BaO₁₀–PO₄ columnar arrangement characteristic for palmierite-supergroup minerals. A tetrahedrally coordinated site is generally occupied by P⁵⁺ but can be partially substituted by V⁵⁺ and S⁶⁺. This substitution is shown in the Raman spectrum of mazorite, which reveals bands that can be assigned to the stretching and bending vibrations of (PO₄)^3–, (VO₄)^3– and (SO₄)^2– groups. The Raman spectra of mazorite from two localities (Hatrurim and Bellerberg) and spectra of minerals belonging to the mazorite Ba₃(PO₄)₂ to gurimite Ba₃(VO₄)₂ solid-solution series are presented. The gradual shift of the Raman bands, caused by cation substitutions, is well observed. The high V⁵⁺ → P⁵⁺ substitution is also observed for gurimite, for which the first X-ray structural data are also presented. Mazorite and other Ba-bearing minerals crystallised from a small portion of residual melt enriched in incompatible elements, such as Ba, V, P, U, S, Ti and Nb, at a temperature of ∼1000°C.